internet connection issues.?

[Aj]

I have at&t uverse internet at 20mbps. Over the past few months on my laptops the internet has gotten slower and more unstable. It takes forever to load pages, or it won't load them at all, youtube videos buffer fast then you see the bar stop buffering, I need to refresh about 8 times to finish one video or turn off my wireless connection and turn it back on. Everytime I do a speed test its always at 20mbps. So why is it doing this? With my mobile devices the internet is perfectly fine, no videos ever buffer and pages load very fast. It's only my computers that have this problem.